1. Field of the Invention
The invention relates to a method for controlling the inking in an offset press, wherein the inking unit has inking zone actuating elements which control zonal inking of a printing material printed with a subject and measurement regions.
2. Description of the Related Art
During printing, a printing material is moved successively through a plurality of printing units of a press, a printing ink normally being applied to the printing material in each printing unit. During collective autotype printing, as a rule the four primary colors black, magenta, cyan and yellow and, if appropriate, special colors are printed, there being a separate printing unit and therefore inking unit for each of these printing inks. The inking unit of a each printing unit has an ink metering device, the ink metering device comprising a number of inking zone actuating elements corresponding to the number of inking zones. The inking zone actuating elements are also designated ink slides or ink knives. Depending on the position of the inking zone actuating elements, printing ink is applied to an ink fountain roll, which is also designated a ductor roll. The quantity of ink applied to the ductor roll for each inking zone as a function of the inking zone actuating elements is transferred by a vibrator roll or film roll to an inking unit roll of the inking unit, which is arranged downstream of a vibrator roll or film roll. The printing ink is moved via a plurality of inking unit rolls in the direction of a forme cylinder or plate cylinder of the respective printing unit. At least one inking unit roll of the respective inking unit, serving as an ink applicator roll, rolls on the forme cylinder of a printing unit. Via the or each ink applicator roll, the printing ink accordingly arrives on at least one printing plate positioned on the forme cylinder. What is known as a transfer cylinder or rubber-covered cylinder interacts with the forme cylinder and transfers the printing ink from the forme cylinder to the printing material.
The color configuration of a printed product to be printed is defined in a prepress stage, as it is known. In this case, for example for all the printing inks to be printed and therefore for all the inking units of the press involved in the printing, what are known as area coverage values are defined for each inking zone. On the basis of these area coverage values, the inking zone actuating elements are set and therefore the zonal inking is determined.
From the prior art, it is already known to measure the inking established on the printing material during printing and, on this basis, to control the zonal inking of the inking units involved in the printing. To this end, measurement regions printed on the printing material outside a subject, what are known as print control elements, are usually measured, in this case actual values of the zonal inking determined being transmitted to a control device of the press. In the control device, the actual values are compared with predefined intended values in order to generate actuating signals for the inking zone actuating elements on the basis of the comparison between the actual values and the intended values and therefore on the basis of the control deviation between the measured actual values and the predefined intended values. In this way, automatic control of the zonal inking is already possible. It is also possible to measure regions within a subject as measurement regions and to control the zonal inking on this basis. In addition, print control elements printed outside a subject as measurement regions and regions within the subject can be measured.
When controlling the zonal inking on the basis of the measurement of print control elements, for example printed outside the subject, it is possible that, although the measured actual values agree with the predefined intended values for all the measurement regions, a deviation between actual values and intended values can be detected in the actual subject for individual separations of the inking. Hitherto, no methods for controlling the inking have been known which take account of this phenomenon.
On this basis, the present invention is based on the problem of providing a novel type of method for controlling the inking in an offset press.